Try this:
[X,Y] = meshgrid(-1:0.01:1);
R = sqrt(X.^2 + Y.^2) + eps;
Z = (2/pi)*((acos(R))-(R).*sqrt(1-(R).^2));
figure
mesh(X, Y, abs(Z))
grid on
then modify the code to get the plot in the image, for example:
Z = (2/pi)*((acos(R))-(R).*sqrt(1-(R).^2)) .* (R <= 1);
Experiment to get the result you want.
